The present invention relates to a vacuum switching tube having contacts which are arranged movably relative to each other within an evacuated housing, and to a current lead for at least one of the contacts having a core and a conductor surrounding the core to provide a helical current path.
A vacuum switching tube having contacts relatively movably arranged in an evacuated housing is disclosed in DE-OS No. 3 033 632. A helical current path is provided by a current lead to one of the contacts having a core and a conductor surrounding the core. The helical current path produces a current-dependent magnetic field which is effective during switching between the separated contacts and has an advantageous effect on switching capacity. The advantageous properties produced by a helical current path, especially those produced by axially-directed magnetic fields in vacuum switching tubes, are counterbalanced by the difficulty in realizing the helical current path in a technically effective and economically advantageous manner. For example, fastening a helical conductor and mutually bracing its turns presents difficulties because connecting means and supports available for this purpose are subjected to considerable thermal and mechanical stresses. In particular, thermal expansions and corresponding mechanical stresses occur during operation, in addition to which are mechanical shock forces and additional electrodynamic forces occurring during switching.
It is known to realize a helical current path along a current lead of a vacuum switching tube by cuts made at the circumference of the current lead which are offset relative to each other (U.S. Pat. No. 3,158,722). The effectiveness of this arrangement, however, is limited by the fact that the cuts cannot be made to any desired depth in view of the required mechanical strength of the current lead. Additionally, associated with making the cuts, even if they are straight and extend perpendicularly to the longitudinal axis of the current lead, is a rather elaborate chip-removing machining operation. Cleaning and degassing the machined parts present additional problems.